arXiv subjects

Henrik Schmidt

Publications and source records attributed to Henrik Schmidt.

6 recordsLinked to original sources

arXiv2025

A User-Centered Teleoperation GUI for Automated Vehicles: Identifying and Evaluating Information Requirements for Remote Driving and Assistance

Teleoperation emerged as a promising fallback for situations beyond the capabilities of automated vehicles. Nevertheless, teleoperation still faces challenges, such as reduced situational awareness. Since situational awareness is primarily built through the remote operator's visual perception, the Graphical User Interface (GUI) design is critical. In addition to video feeds, supplemental informational elements are crucial - not only for the predominantly studied Remote Driving but also for the arising desk-based Remote Assistance concepts. This work develops a GUI for different teleoperation concepts by identifying key informational elements during the teleoperation process through expert interviews (N = 9). Following this, a static and dynamic GUI prototype is developed and evaluated in a click-dummy study (N = 36). Thereby, the dynamic GUI adapts the number of displayed elements according to the teleoperation phase. Results show that both GUIs achieve good System Usability Scale (SUS) ratings, with the dynamic GUI significantly outperforming the static version in both usability and task completion time. The User Experience Questionnaire (UEQ) score shows potential for improvement. To enhance the user experience, the GUI should be evaluated in a follow-up study that includes interaction with a real vehicle.

cs.HC↗

arXiv2021

Synchronous-Clock Range-Angle Relative Acoustic Navigation: A Unified Approach to Multi-AUV Localization, Command, Control and Coordination

This paper presents a scalable acoustic navigation approach for the unified command, control and coordination of multiple autonomous underwater vehicles (AUVs). Existing multi-AUV operations typically achieve coordination manually, by programming individual vehicles on the surface via radio communications, which becomes impractical with large vehicle numbers; or they require bi-directional inter-vehicle acoustic communications to achieve limited coordination when submerged, with limited scalability due to the physical properties of the acoustic channel. Our approach utilizes a single, periodically-broadcasting beacon acting as a navigation reference for the group of AUVs, each of which carries a chip-scale atomic clock (CSAC) and fixed ultra-short baseline (USBL) array of acoustic receivers. One-way travel-time (OWTT) from synchronized clocks and time-delays between signals received by each array element allows any number of vehicles within receive distance to determine range, angle, and thus determine their relative position to the beacon. The operator can command different vehicle behaviors by selecting between broadcast signals from a predetermined set, while coordination between AUVs is achieved without inter-vehicle communication, by defining individual vehicle behaviors within the context of the group. Vehicle behaviors are designed within a beacon-centric moving frame of reference, allowing the operator to control the absolute position of the AUV group by re-positioning the navigation beacon to survey the area of interest. Multiple deployments with a fleet of three miniature, low-cost SandShark AUVs performing closed-loop acoustic navigation in real-time provide experimental results validated against a secondary long-baseline (LBL) positioning system, demonstrating the capabilities and robustness of our approach with real-world data.

cs.RO↗

arXiv2021

Flow profiles near receding three--phase contact lines: Influence of surfactants

The dynamics of wetting and dewetting is largely determined by the velocity field near the contact lines. For water drops it has been observed that adding surfactant decreases the dynamic receding contact angle even at a concentration much lower than the critical micelle concentration (CMC). To better understand why surfactants have such a drastic effect on drop dynamics, we constructed a dedicated a setup on an inverted microscope, in which an aqueous drop is held stationary while the transparent substrate is moved horizontally. Using astigmatism particle tracking velocimetry, we track the 3D displacement of the tracer particles in the flow. We study how surfactants alter the flow dynamics near the receding contact line of a moving drop for capillary numbers in the order of $10^{-6}$. Even for surfactant concentrations $c$ far below the critical micelle concentration ($c \ll$ CMC) Marangoni stresses change the flow drastically. We discuss our results first in a 2D model that considers advective and diffusive surfactant transport and deduce estimates of the magnitude and scaling of the Marangoni stress from this. Modeling and experiment agree that a tiny gradient in surface tension of a few $μN \, m^{-1}$ is enough to alter the flow profile significantly. The variation of the Marangoni stress with the distance from the contact line suggests that the 2D advection-diffusion model has to be extended to a full 3D model. The effect is ubiquitous, since surfactant is present in many technical and natural dewetting processes either deliberately or as contamination.

physics.flu-dyn↗

arXiv2019

Versatile high-speed confocal microscopy using a single laser beam

We present a new flexible high speed laser scanning confocal microscope and its extension by an astigmatism particle tracking device (APTV). Many standard confocal microscopes use either a single laser beam to scan the sample at relatively low overall frame rate, or many laser beam to simultaneously scan the sample and achieve a high overall frame rate. Single-laser-beam confocal microscope often use a point detector to acquire the image. To achieve high overall frame rates, we use, next to the standard 2D probe scanning unit, a second 2D scan unit projecting the image directly on a 2D CCD-sensor (re-scan configuration). Using only a single laser beam eliminates cross-talk and leads to an imaging quality that is independent of the frame rate with a lateral resolution of 0.235\unit{μm}. The design described here is suitable for high frame rate, i.e., for frame rates well above video rate (full frame) up to a line rate of 32kHz. The dwell time of the laser focus on any spot in the sample (122ns) is significantly shorter than in standard confocal microscopes (in the order of milli or microseconds). This short dwell time reduces phototoxicity and bleaching of fluorescent molecules. The new design opens further flexibility and facilitates coupling to other optical methods. The setup can easily be extended by an APTV device to measure three dimensional dynamics while being able to show high resolution confocal structures. Thus one can use the high resolution confocal information synchronized with an APTV dataset.

physics.optics↗

arXiv2018

Scanning tunneling spectroscopy investigations of superconducting-doped topological insulators: Experimental pitfalls and results

Recently the doping of topological insulators has attracted significant interest as a potential route towards topological superconductivity. Because many experimental techniques lack sufficient surface sensitivity, however, a definite proof of the coexistence of topological surface states and surface superconductivity is still outstanding. Here we report on highly surface sensitive scanning tunneling microscopy (STM) and spectroscopy (STS) experiments performed on Tl-doped Bi$_2$Te$_3$, a three-dimensional topological insulator which becomes superconducting in the bulk at $T_{\rm C} = 2.3$\,K. Landau level spectroscopy as well as quasiparticle interference mapping clearly demonstrated the presence of a topological surface state with a Dirac point energy $E_{\textrm{D}} = -(118 \pm 1)$\,meV and a Dirac velocity $v_{\textrm{D}} = (4.7 \pm 0.1)\cdot 10^{5}$\,m/s. Tunneling spectra often show a superconducting gap, but temperature- and field-dependent measurements show that both $T_{\rm C}$ and $μ_0 H_{\rm C}$ strongly deviate from the corresponding bulk values. Furthermore, in spite of acritical field value which clearly points to type-II superconductivity, no Abrikosov lattice could be observed. Experiments performed on normal-metallic Ag(111) prove that the gapped spectrum is only caused by superconducting tips, probably caused by a gentle crash with the sample surface during approach. Nearly identical results were found for the intrinsically n-type compound Nb-doped Bi$_2$Se$_3$. Our results suggest that the superconductivity in superconducting-doped V-VI topological insulators does not extend to the surface where the topological surface state is located.

cond-mat.supr-con↗

arXiv2016

Robust spin-polarized midgap states at step edges of topological crystalline insulators

Topological crystalline insulators are materials in which the crystalline symmetry leads to topologically protected surface states with a chiral spin texture, rendering them potential candidates for spintronics applications. Using scanning tunneling spectroscopy, we uncover the existence of one-dimensional (1D) midgap states at odd-atomic surface step edges of the three- dimensional topological crystalline insulator (Pb,Sn)Se. A minimal toy model and realistic tight- binding calculations identify them as spin-polarized flat bands connecting two Dirac points. This non-trivial origin provides the 1D midgap states with inherent stability and protects them from backscattering. We experimentally show that this stability results in a striking robustness to defects, strong magnetic fields, and elevated temperature.

cond-mat.mes-hall↗